So we have no disclosures relevant to this talk. Posterior shoulder instability has been increasingly recognized as being more common with between 10 and 27% of young athletes and military population having some degree of posterior shoulder instability. We know that glenoid and acromial morphology has been suggested to have a role in failure following posterior shoulder stabilization procedures. But there's been limited data on the effectiveness of nonoperative treatment overall and the role of glenoid and acromial morphology in nonoperative treatment. So the purpose of this study was to overall determine the rate of failure in nonoperative treatment of posterior shoulder instability in a young and active population, to evaluate glenoid and acromial morphologic factors that contribute to failure and then evaluate additional injury patterns on serial MRI for those that have serial MRI following failure of nonoperative treatment. This was a retrospective review. Posterior shoulder instability was defined as having a history consistent with posterior subluxation or dislocation, as well as a positive exam, including Jerk and Kim test, with MRI demonstration of an isolated posterior labral tear. Patients were excluded if they had any combined labral tear, prior stabilization procedures, multidirectional instability or incomplete follow-up. In total, we had 123 patients that were treated nonoperatively for posterior shoulder instability. These were all active duty service members with a minimum of two-year follow-up. Nonoperative criteria was a minimum of six months, activity modification, physical therapy with gradual return to play. And failure was defined as recurrent pain with a positive exam, in addition to having instability and inability to return to activity, requiring either revision surgery or medical discharge from the military second to their shoulder. We evaluated glenoid and acromial morphology. The acromial measurements you can see on the right. These include posterior acromial coverage, acromial tilt and acromial height from left to right there, as well as glenoid retroversion, posterior glenoid bone loss and humeral head subluxation. Overall, 47% of our nonoperatively treated shoulders failed non-op treatment. The mean follow-up was 3.4 years, and these shoulders failed after approximately 545 days. Of those that failed, 79% had surgery, 21% ultimately went medical discharge from the military. When we look at the risk factors, there is no association with gender, duration of symptoms, mechanism of injury or type of instability with failure of nonoperative treatment. When we look at the risk factors for glenoid and acromial morphology, posterior acromial height, posterior humeral head subluxation and posterior glenoid bone loss were all significantly associated with failure of nonoperative treatment. When we look at 17 patients that had serial MRI after failure of nonoperative treatment, we see that over a period of 488 days from index to repeat MRI, bone loss increased from 2.7% to 6.5%. So in the current study, 47% of patients had failed nonoperative treatment after six months of treatment. Risk factors include greater posterior acromial height, greater posterior humeral head subluxation ratio and posterior glenoid bone loss. And of those that failed with serial MRI, we saw increased posterior glenoid bone loss from 2.7% to 6.5%. When we look at the literature, Dominic Meyer and Christian Gerber looked at acromial morphology in patients that were treated with either anterior or posterior instability. They demonstrated in their series that posterior acromial height was the strongest association with the direction of instability. And so this study supports that finding with posterior acromial height in our study being the strongest predictor of failure for nonoperative treatment. And when we look at two recent studies for posterior glenoid bone loss, Adam Hines and J.T. Tokish found that in theirs undergoing arthroscopic posterior stabilization, the mean posterior glenoid bone loss was 7.3%. There was no association with WOSI scores or return to duty in those that had bone loss versus those that did not. Then in a series that we had done out of the military as well, we found an overall incidence of measurable posterior glenoid bone loss of 59%. 14% had subcritical bone loss. We did find that this influenced their ability to return to duty. And this is also consistent with the present study which showed that failure of nonoperative treatment increased posterior glenoid bone loss by about 4%. So in conclusion, nonoperative treatment of posterior instability can result in failure of approximately 50%, increased posterior acromial height, greater posterior humeral head subluxation, and the percentage of posterior glenoid bone loss are risk factors for nonoperative failure. And failure of nonoperative management is associated with progressive bone loss of approximately 4%. Thank you. Dr. Walts will be speaking regarding biomechanical evaluation of posterior shoulder instability and a clinically relevant posterior bone loss model.

posterior shoulder instability

nonoperative treatment

failure rate

glenoid and acromial morphology

serial MRI